Super economical wave piercing catamaran cruisers

Thanks Ken, Mainly a legitimising ploy - "staying on thread?"

 

Good move, thanks for keeping me on-topic!

I often see these threads drifting on and off topic. I would create a new thread for the Derby Gravel Truck if the plans were finished, or if it were my goal to discuss the boat further. But right now they are not and I am not. I only wanted to mention the boat in passing at this time, in case others might find it interesting.

I think the DGT is a boat worthy of future discussions, and after Jeff finishes the plans I'm hoping to build one, assuming I still have the same interest in the design then as now. That's the time when it 'makes sense' to give the boat it's own thread ...

I posted the pix in my own boatdesign.net gallery yesterday and already someone has emailed me to ask me if plans are available. This is probably why Jeff has posted the pix only in his [jgbuilders] Yahoo group -- so he would not have to respond to numerous inquiries from others until he actually has the plans finished and ready for sale.

 

Ken, you are always welcome to use "Grumpy...." thread (saves me looking all around)

 

Latest Goldcoast 50 WP

This is my boat:

http://pmyeditors.blogspot.com/2008/01/is-it-finally-happening-are-power.html

Be happy to discuss with anyone interested.

Currently at Goldcoast here in St. Croix nearing completion. I took it out several times before some of the systems were in place (head, generator, etc.) with excellent results.

Didn't notice any high speed calm water issues cruising at 24 kts burning under 15 gph apart from some spray from the bows misting the upper deck.

No spray at 20kts or less, and the leading edges of the bows are now being 'sharpened' to reduce drag and spray some, and an upper helm windshield is being installed as well.

 

Warren, How will you go in the following "challenge"? http://www.icecat.com.au/trial.htm - at the bottom of this page. This boat has achieved http://www.icecat.com.au/summary.htm a pretty impressive performance - fuel economy wise.

I reckon with current technology, 800 ml per nautical mile is do-able for a vessel capable of travelling 2,500 miles non-stop at around 12 to 15 knots. as per the "challenge criteria". How will yours go?

 

Hi!

Notes taken during the first sea trial show 3 gallons per hour at 10 kts (which looks like about 1 litre per mile?) and a max range of just under 2,500 miles with full tanks (600 gallons).

The conditions were pretty rough, 20+ kt winds, 6-8 ft seas, etc, so should be a touch better in calmer conditions?

Also, the sharpened bows should help a tad?

Weight should be about the same as a large pile of mechanics tools gets replaced by an upscale but lighweight interior trim package.

There was also about 200 gallons of fuel aboard (max is 600 gallons) and 10 of us aboard.

At 15 kts fuel burn doubled to about 6 gal. per hour so that means a max range of about 1,800 miles.

Not sure what the refueling rules are?

Looks close to or better than the Icecat design?

Also, with twin 190 hp vs twin 100 hp diesels and a higher bridge deck height above the water I can crank it up and cruise at 25kts all day into 6 ft seas as needed?

I also have two helms, 3 queen berths, and relaxed seating for 20 outside, and about the same inside.

Last, seems the beam on Icecat is wide enough for some uncomfortable 'snap roll?' Goldcoast kept mine down to 17 ft. to minimize it for passenger comfort.

 

WPC design

The design of the cats in St. Thomas are interesting and time tested for reliability. As mentioned in the first part of the thread, the design is for a long distance WP cruiser and one that would be the most efficient in fuel consumption and designed for ICW or waters of moderate wave conditions. It is assumed that a long distance cruiser would probably only be carrying 2 to 4 people at most. The goal here is to design the wave peircing cat cruiser that has a non-refueling range that would take it from Key West to New York. 1200 statute miles. Of all interesting hull designs, it is believed that a wave piercing cat has the best chance of doing the task with the least amount of fuel and at "reasonable" speeds. We aren't looking for engines in the hundreds of horsepower, but lesser hp with more efficient engines.....possibly a diesel outboard. With today's high fuel prices that continually move higher, hull and power plant efficiency are becoming more crucial for those who want to cruise, but are limited to a normal family budget. The end goal is for a wave piercing cat that can accommodate a max of 4 people in relative comfort and burn approximately 200 gallons of fuel for the 1,200 trip at a max of around 18 to 20 knots and leave no wake. Rather than spend big bucks on a preliminary design, building a large model first would be the best and least expensive method to achieve, "proof of concept" with a design. YOUR THOUGHTS?

 

My boat both fits that deiscription and more. Fuel efficiency won't increase with a lower hp diesel, unless the package is lighter, and the 190 hp Volvo d3 package with stern drive is only about 750 lbs per engine. Lesser hp doesn't mean more efficient, for all practical purposes. And the (composite) stern drive means no rudder and minimal underwater drag, and the blades tilt out of the water for overnighting.

It's perfect for 2-4 people, as the unused berths make for welcome, massive storage useful on long trips.

It can make the 1,200 mile trip on a 600 gallon tankful at 25 kts, and about half a tank at 'cruiser' slower speeds.

And virtually no wake at any speed.

Draft is under 2 ft, and the legs 'kick up' if they hit anything.

 

WP Boat

Your boat is really great and performs well, but I hate to think of what one like it would cost. Definitely not for the home builder of course, but still close to what we're looking for.

 

Some nice pictures in the links of this thread.

Look for them in the Random Picture thread.

 

50 Wp

I think the basic boat can be had for about $500,000, but it's easy to spend more than double that on electronics, fancy lighting, appliances, fancy paint, interior trim, high end fixtures, teak decking, etc. etc. etc. etc. etc. etc....

Another nice feature I forgot to mention is the main cabin a/c is a roof top 110v (about 1.8 kw) Seamax RV type unit that costs about $900. With the shades down it readily cools the whole cabin and the cold air also quickly works it's way to the lower berths.

Goldcoast sells the basic 'ferry' for about $450,000 with 225 hp outboards, with a single helm, single head, commercial white paint, etc. The D3 diesels shouldn't add more than about 25,000.

 

Good information

Thanks Warren for the cost data. I suspected that the ferries would be in that price range. Gold Coast is a leader in the field of wave piercing cats that is close enough to be able to see some of their boats. I believe that what I'm really looking for is construction drawings for the less affluent to be able to build their own wave piercing cats from Gold Coast licensed drawings. A half of a million dollars is significantly above the price that most people can pay, but there is a lot of boat building talent out there that can do the job for a fraction of Gold Coast costs. A construction drawing package at reasonable cost may be a product that Gold Coast may want to develop to supplement income and, of course, as more people build the cats, input on innovations would benefit Gold Coast. Just early morning thoughts over coffee.

 

The fundamental problem with 'wave piercing' hull designs is that the reduced water plane and volume (what allows them to 'pierce' waves under some conditions) is also what contributes to two things that have given them, particularly the larger ones, their bad motion sickness characteristics:

1. Natural period of pitch is reduced compared to a stiffer hull form. Humans are most susceptible in terms of seasickness to periods in the 8-10-second range.

2. Damping is less..so when the wavepiercing hulls are operating in wave conditions where pitch resonance is excited..the pitch amplitudes are larger than those for a stiffer hull.

For most wavepiercers, their most spectacular 'piercing' behavior is observed when resonant pitching ultimately results in stuffing the bow violently and deeply in the the face of a wave. The consequences of such an event have been noted in an earlier post. On the other hand, I've always had a soft spot for wavepiercing cats..if it were not for those, we may never had been prodded to develop such elaborate and expensive active stablization systems in the early 90's that are the norm now on virtually all passenger carrying wavepiercers over 50m that were ever built.

 

50 Wp

two things.

yes, plans are available from Goldcoast. Not sure but probably in the $5,000 range. But that's just a guess.

second:

"For most wavepiercers, their most spectacular 'piercing' behavior is observed when resonant pitching ultimately results in stuffing the bow violently and deeply in the the face of a wave."

This is minimized on mine by having the bows shaped such that they can accelerate vertically with minimal drag, and also the upper bow is extended some and also shaped to provide lift as needed, as well as better protect the windshield.

Also, speed is a big factor. When going into tight, 10 ft head seas a month or so ago with several passengers, at 14 kts i was splashing and slapping some but not enough to do any damage. Slowing to 10 kts took away all the drama. By quartering rather than going straight into the waves 20 kts wasn't any problem, with no slamming or slapping, though a coffee mug would have sloshed the coffee all over the place.

We took 20 people, including several kids under age 10, home from St. John in 8 ft seas quartering all the way with a good time had by all and no one got sick on the two hour ride at 18- 20 kts.

A few weeks later in 3-5 ft head seas/chop, I was able to maintain the 24kt cruise speed without any drama and good stability.

Attached is a picture taken during construction and a computer generated model done before the design was finalized.

 

Wave piercing cat

A 45 foot wave piercer I designed a couple of years ago.

Grahame Shannon
Avia Design Group